“Drilling mud” is a generic term for a fluid containing dispersed solids which is used in the drilling of wells. Drilling mud, comprising various chemical compounds, is pumped down the drill string during the drilling of a well to assist, among other things, in cooling the drill bit, minimizing corrosion of drill pipe, pressurizing the well against hydrostatic head when the drill string enters a pressurized formation, and further to carry drill chips away from the drill bit, which then become suspended in such drilling mud. The drilling mud flows back to surface, typically in the annulus between the drill string and the well casing.
When a hydrocarbon-containing strata is encountered during drilling of a well, a certain amount of the gas containing hydrocarbons from the strata will be entrained in the drilling mud and thus be carried to the surface by the drilling operation. Thus any entrained gas, when extracted from the drilling mud, can be analyzed and used to determine the presence of hydrocarbon and the likely “quality” of the hydrocarbon-bearing formation (ie provide an estimate of the quantum of hydrocarbon in the strata being drilled through) at the depth of the well at which such hydrocarbon-bearing strata existed.
The above procedure is known as “mud logging” and is a critical process in the drilling of wells for determining if the drilled well has successfully encountered a “rich” hydrocarbon-containing formation, the “quality” of the formation, and the depth at which such hydrocarbon-bearing formation was encountered.
Gas trap devices for facilitating the liberation of gases from drilling mud and collecting such gases during drilling for subsequent analysis in mud-logging operations are well known in the mud-logging industry.
Such prior art gas trap devices are typically mounted on “mud tanks”, and serve to: (i) agitate the mud collected in such tanks from a well being drilled in order to liberate any gas entrained therein; and (ii) collect such liberated gas from the agitated mud and direct such collected gas to gas detection and analysis equipment.
One such gas trap device 10 is disclosed in U.S. Pat. No. 5,199,509 entitled “Controlled Gas Trap System”, assigned to Texaco Inc. Such gas trap device 10, as shown in FIG. 1 thereof, possesses a cylindrical trap body 12 closed at its upper end by plate 14 and at its lower end by a plate 16 having a central annular aperture 18 which is co-axial with the housing 12, with plates 16 and 20 defining a mixing chamber 24 therebetween. A constant speed motor 26 is mounted co-axially on the top plate 14, and a downwardly-extending vertical shaft 30 of the motor extends downwardly into the interior of the housing 12. An agitator 42 is connected to the bottom of the shaft 30 and lies in the mixing chamber 24. Agitator 42 possesses a series of legs 44, 46, 48 (“beater bars”) which when rotated by shaft 30 serve to agitate drilling mud to thereby liberate any entrained gas, which is collected via sample line 34 for analysis.
Another similar prior art gas trap is that taught in U.S. Pat. No. 5,648,603, likewise assigned to Texaco Inc., which discloses a similar gas trap 11 having a similar plurality of legs 18, which collects liberated gas from agitated drilling mud in head space 21, with the added feature of providing a standard gas from a standard gas source 27 (a pressurized tank). The flow of standardized gas is calibrated, to assist in error correction with regard to the sampled (liberated) gas stream.
U.S. Pat. No. 6,389,878 teaches a similar type of gas trap 1, possessing a modification wherein the shaft 43 extending downwardly from motor 41 is hollow, with radially-extending tubes 44 extending radially outwardly therefrom, which serve to inject “stripping” air into the drilling mud, which air is drawn (along with gas entrained in the mud) upwardly within the gas trap for subsequent collection via tube 20 and thereafter compositional analysis. Significantly, US '878 expressly teaches that the gas trap 1 is comprised of an upper and lower canisters 13, 12, respectively, each of which is a truncated right circular cone. The truncated open end 19 of the upper canister 13 is smaller than the truncated open end 15 of the lower canister 12 so that it is partially insertable into lower canister 12. The upper and lower canisters 13, 12 are sealably joined at their connective interface 23. No means of quick release of one canister from the other is taught or suggested.
US Patent Publication 200910077936 teaches a similar gas trap, with the added feature that such gas trap is vertically variably positionable. Significantly, the container 16 which contains the stirrer 32, appears to be a unitary construction, with no disclosure of means to access the stirrer 32 in the event replacement is required.
Problematically, due the drilling mud containing significant abrasives, not the least of which is drill chips entrained therein from drilling operations, as well as having (and being designed to entrain therewithin) suspended solid particles, such drilling mud and abrasive particles therein causes serious and substantial wear to rotating outwardly-radially extending “beater bars” on the agitator shaft, frequently resulting (depending on the speed of rotation of the shaft and the amount of abrasives contained in the drilling mud) in breakage and/or substantial material loss of the beater bars, all of which result in ineffective or reduced effective operation of the agitation of the drilling mud and thus the gas trap, requiring servicing of or replacement of the shaft and/or one or more beater bars of the gas trap.
Thus a significant disadvantage of each of the prior art gas traps and their designs is that the container (or plates) which surround the shaft make replacement or access to the shaft difficult or impossible.
Similarly, prior art gas traps sold by RigSat Communications Inc. (the within application assigned to such entity) possessed a bottom member which surrounded the shaft and beater bars, which was releasably secured to a top section on which the motor was mounted by means of threaded bolts and mating threaded apertures. Although such design, being of a two part construction, allowed access to the shaft upon removal of the threaded bolts, such was time consuming and often resulted in loss of bolts within the mud tanks upon which the gas traps were mounted.
Accordingly, a real need exists in the prior art for a gas trap of two-part construction, which allows ready and easy access to beater bars to adequately service or replace such shafts and/or beater bars, in order to reduce maintenance costs (and “down” time) of existing gas traps in mud logging operations.